Starlin has more than once written Thanos as failing/losing. Like you said, the Thor loss was not bad and had heavy context to it. And like you said, the Ka-Zar fight is misrepresented itself. Ka-Zar does not defeat Thanos in battle. He just performs better than he should have in one scene.

I believe that Starlin mostly wanted to keep continuity in line with his previous theme of Thanos no longer being a nihilist. He actually retconned an Avengers issue whereas Thanos doesn't lose and has high power showings. But he was a nihilist in that issue.

Starlin basically retcons two "losses" and does both in one book on one page. Yet some will make it out as if he has individually retconned double digit losses.

As far as Slott, his whole things was basically making fun of the retcons.

But thats the thing though. Why did they feel the need to retcon the Thor fight as being a clone?

With Thor's history, and what he unleashed in their encounter, was it unbelievable to just let Thanos loose that one?

At some point it just becomes ridiculous to protect a character fight record like that. That the writer of the Squirrel girl story thought necessary (and funny) to include a Watcher to certify it was *THE* Thanos says a lot about the level of protectionism in the air. It was almost like they needed to laught at it a bit.